Azeotropes of 2-methylbutane and 1,1-dichloro-1-fluorethane and the use thereof in the production of rigid foams

ABSTRACT

The present invention is directed to a novel azeotrope consisting essentially of from 25 to 35% by weight of 2-methylbutane and from 65 to 75% by weight of 1,1-dichloro-1-fluoroethane, and the use thereof in the production of rigid, closed cell foams.

BACKGROUND OF THE INVENTION

The use of trichloromonofluoromethane ("CFC-11") in the production of closed cell, rigid polyurethane and polyisocyanurate foams is well known (see, e.g., U.S. Pat. Nos. 3,072,582; 3,091,551; 3,153,002; 3,524,825; 3,846,347; and 4,248,975). Recently, the urethane foam industry has been investigating methods for reducing the amount of CFC-11 used in producing rigid foams.

U.S. Pat. No. 3,745,203 describes the production of polyurethane moldings using a mixture of two volatile blowing agents. The least volatile of the blowing agents has a boiling point of from 30° F. to 120° F., while the more volatile blowing agent in the mixture has a boiling point of from -50° F. to 500° F. The difference between the boiling points of the two blowing agents in the mixture is from 30° F. to 150° F.

German Auslegeschrift 1,288,312 describes the use of an azeotrope of CFC-11 and isopentane as a blowing agent (U.S. Pat. No. 3,249,546 describes the azeotrope itself).

U.S. Pat. No. 4,055,521 describes a blowing agent which is a mixture of CFC-11, isopentane, and methylene chloride.

U.S. Pat. No. 3,391,093 describes the use of halogenated blowing agents which generally have boiling points below about 80° F. for producing polyurethane foams. The reference does indicate that low molecular weight hydrocarbon gases can be used with the halogenated blowing agents. U.S. Pat. No. 4,795,763 broadly indicates that mixtures of halohydrocarbons and hydrocarbons can be used as blowing agents for polyurethane foams.

It has also been suggested that 2,2-dichloro-1,1,1-trifluoroethane ("HCFC-123") and 1,1-dichloro-1-fluoroethane ("HCFC-141b") can be used as blowing agents for rigid polyurethane foams (See, e.g., Dishart et al, "The DuPont Program on Fluorocarbon Alternative Blowing Agents for Polyurethane Foams," POLYURETHANES WORLD CONGRESS 1987-SEP. 29-OCT. 2, 1987, pages 59-66, and U.S. Pat. No. 4,076,644).

The use of a mixture of a chlorofluorocarbon having an atmospheric boiling point of from about 74° F. to about 120° F. and an alkyl alkanoate having a molecular weight of no more than about 88 as a blowing agent has been described in U.S. application Ser. No. 321,032, filed on Mar. 9, 1989. Among the chlorofluorocarbons described are HCFC-123 and HCFC-141b. Among the alkyl alkanoates described is methyl formate.

Finally, various compositions based on halogenated hydrocarbons are known for use as cleaning solvents. For example, U.S. Pat. No. 4,055,507 describes the use of an azeotropic mixture of 1,2-dichloro-1,1-difluoroethane and 3-methylpentane. Japanese 1,141,995 (abstract only) describes an azeotropic mixture of 67 to 87% by weight of HCFC-123 and 13 to 33 % by weight of 2-methylbutane. Japanese 1,141,996 (abstract only) describes an azeotropic mixture of HCFC-141b and a member selected from the group n-pentane, 2-methylbutane and 2,2-dimethylbutane.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graph showing a plot of the mole fraction of 2-methylbutane in the liquid phase versus the mole fraction of 2-methylbutane in the vapor phase of a mixture refluxing at steady state at one atmosphere.

DESCRIPTION OF THE INVENTION

The present invention is directed to an azeotropic composition which is eminently suitable for production of rigid foams. In addition, the azeotropic compositions of the present invention are well suited for solvent cleaning applications. More particularly, the present invention is directed to an azeotrope-like composition consisting essentially of from 25 to 35% by weight of 2-methylbutane and from 65 to 75% by weight of 1,1-dichloro-1-fluoroethane.

The compositions of the present invention consist essentially of 2-methyl butane (b.p. 28° C.) and 1,1-dichloro-1-fluoroethane (b.p. 32° C.). This latter material is known in the nomenclature conventional in the chlorofluorocarbon field as hydrochlorofluorocarbon 141b. The 2-methylbutane used can be of normal commercial purity which typically contains at least 95% 2-methylbutane. The present mixture of 25 to 35% 2-methylbutane and 65 to 75% 141b is azeotropic in nature in that compositions within this range exhibit a substantially constant boiling point. Being substantially constant boiling, the mixture does not tend to fractionate to any great extent upon evaporation. After evaporation, only a small difference exists between the composition of the vapor phase and the composition of the initial liquid phase. This difference is so small that the compositions of the vapor and liquid phases are considered substantially identical. Accordingly, any mixture within the above noted range exhibits properties which are characteristic of a true binary azeotrope. Compositions consisting essentially of from 27 to 33% by weight 2-methylbutane and 67 to 73% by weight of 141b have been found to exhibit particularly satisfactory performance. The composition consisting of 30.4% by weight of 2-methylbutane and 69.6% by weight of 141b has been established, within the accuracy of the boiling point determination procedure, as the true binary azeotrope with a boiling point of about 25.7° C.

The drawing shows a graph plotting the mole fraction of 2-methylbutane in the liquid phase versus the mole fraction of 2-methylbutane in the vapor phase of a mixture refluxing at steady state at 1 atmosphere. These mole fractions were obtained by gas chromotography and were adjusted to be quantitative by using a calibration curve as described below. The point at which this mole fraction curve crosses the line with slope 1 and intercept 0 is, by definition of an azeotrope, the true binary azeotropic composition.

A series of blends of 2-methylbutane with 141b were prepared from 0 to 100 mole percent of 2-methylbutane in 10% increments. First, each blend was injected into a Perkin-Elmer Gas Chromatograph ("GC") to establish a correlation between relative peak areas versus actual molar concentrations. This procedure was done by making duplicate blends and measuring each blend twice. This established the calibration curve as well as a 95% confidence interval which was used to establish the error about the expected azeotropic composition. Secondly, each blend was gently heated in a distillation pot and refluxed for 10 minutes in the apparatus described above. The reflux condenser was kept at 10° C. and was open to the atmosphere through a drying tube. Once steady state was achieved, samples of the liquid and vapor were taken through the sample ports in the apparatus, with the liquid samples being taken from the distillation pot and the vapor samples taken at the base of the the condenser. Liquid and vapor temperatures were also taken from the pot and from a point between the pot and the condenser and were recorded. Duplicate samples were injected into the GC and the relative peak areas recorded. These relative peak areas were converted to mole fractions using the calibration curve. The data was plotted with the resultant graph being shown in the drawing. An azeotrope is defined as the mixture of liquids where, at the boiling point, the concentration of the components is the same in the liquid and vapor phases. Therefore, the point at which the mole fraction plot crosses the line of slope 1 and intercept 0 is the expected azeotropic composition.

The compositions are suitable for solvent cleaning applications and as blowing agents for rigid foams.

The present invention is also directed to the discovery that the azeotrope described herein is eminently suitable for the production of closed cell, rigid foams. The resultant foams are substantially lower in density than foams produced from trichloromonofluoromethane alone, yet still have relatively low K-factors. More particularly, the present invention is directed to an improved process for the preparation of closed cell rigid foams. The process broadly comprises reacting a) a polyol component having a hydroxyl number of from about 200 to about 650, and b) an organic polyisocyanate, in the presence of c) a catalyst, d) a foam stabilizer, and e) a blowing agent. The improvement resides in the use of the azeotropic mixture herein as the blowing agent.

The polyols, isocyanates, catalysts, and foam stabilizers useful herein and the various methods of combining them to produce closed cell, rigid foams are generally known in the art.

The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.

EXAMPLES

In the examples which follow, the following materials were used:

    ______________________________________                                         POLYOL A:  a 460 OH number polyol prepared by                                             sequentially reacting 1 mole of an 80/20                                       mixture of 2,4- and 2,6-toluene diamine                                        with about 3.7 moles of ethylene oxide and                                     then about 3.3 moles of propylene oxide.                            POLYOL B:  a 395 OH number polyol prepared by                                             sequentially reacting 1 mole of a mixture                                      of 2,3- and 3,4-toluene diamine with about                                     3.5 moles of ethylene oxide and then with                                      about 4.5 moles of propylene oxide.                                 HCFC-141b: 1,1-dichloro-1-fluoroethane.                                        2-MB:      2-methylbutane.                                                     L-5440:    a polyalkyleneoxidedimethylsiloxane                                            copolymer, commercially available from                                         Union Carbide.                                                      PMDTA:     pentamethyldiethylenetriamine.                                      TMEDA:     tetramethylethylenediamine.                                         ISO:       Mondur MR isocyanate, a commercially                                           available polymethylene polyphenyl                                             polyisocyanate from Mobay Corporation,                                         having an NCO content of about 32%.                                 ______________________________________                                    

In the examples, the HCFC-141b and 2-MB were first mixed. The ingredients listed in the Table under B-side were then blended. The isocyanate was then mixed in a mixing vessel using an air stirrer. After the mix times noted in the Table, the reaction mixtures were poured into a polyethylene lined 101/2"×101/2"×21/2" cardboard box. The cream times, gel times, densities and K-factors of the systems were as reported in the Table. Example 1 was a comparative example.

                  TABLE 1                                                          ______________________________________                                                         1     2                                                        ______________________________________                                         B-SIDE                                                                         POLYOL A, pbw     33.5    33.5                                                 POLYOL B, pbw     33.5    33.5                                                 L-5440, pbw       1.5     1.5                                                  PMTDA, pbw        2.2     2.2                                                  TMEDA, pbw        1.1     1.1                                                  HCFC-141b, pbw    22.4    15.59                                                2-MB, pbw         --      6.81                                                 A-SIDE                                                                         ISO, pbw          70.0    70.0                                                 RESULTS                                                                        Mix time, sec.    5       5                                                    Cream time, sec.  12      9                                                    Gel time, sec.    29      37                                                   Density, pcf.     1.77    1.27                                                 K-Factor          0.125   0.162                                                (BTU-in                                                                        Hr-ft2)                                                                        ______________________________________                                    

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims. 

What is claimed is:
 1. An azeotrope composition consisting essentially of from 25 to 35% by weight of 2-methylbutane and from 65 to 75% by weight of 1,1-dichloro-1-fluoroethane wherein said composition boils at about 25.7° C. at 1 atmosphere.
 2. The composition of claim 1 consisting essentially of from 27 to 33% by weight of 2-methylbutane and from 67 to 73% by weight of 1,1-dichloro-1-fluoroethane.
 3. The composition of claim 2 consisting essentially of 30.4% by weight 2-methylbutane and 69.6% by weight of 1,1-dichloro-1-fluoroethane. 